Re: [song-md:md-next 5/6] drivers/md/raid10.c:1526:8-27: atomic_dec_and_test variation before object free at line 1532.

Hi all

The atomic_t r10_bio->remaining starts at 1 in raid10_handle_discard. It means
raid10_handle_discard uses it and sets it to 1. So in fact it starts at 0 and sets to 1
when it's used at first time. Then r10_bio->remaining is added by atomic_inc per usage.

It decrements the value when leaving raid10_handle_discard and in every callback function.
So the count of r10_bio->remaining in this patch is right.

Regards
Xiao

On 03/16/2021 08:29 AM, kernel test robot wrote:

tree:   git://git.kernel.org/pub/scm/linux/kernel/git/song/md.git md-next
head:   49c4d345c81f149a29b3db6e521e5191e55f02b6
commit: f3cf8c2b2caf6ae77b7c786218d3b060faef63a6 [5/6] md/raid10: improve discard request for far layout
config: x86_64-allyesconfig (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>


"coccinelle warnings: (new ones prefixed by >>)"

quoted

quoted

drivers/md/raid10.c:1526:8-27: atomic_dec_and_test variation before object free at line 1532.

    drivers/md/raid10.c:1526:8-27: atomic_dec_and_test variation before object free at line 1537.

vim +1526 drivers/md/raid10.c

   1520	
   1521	static void raid_end_discard_bio(struct r10bio *r10bio)
   1522	{
   1523		struct r10conf *conf = r10bio->mddev->private;
   1524		struct r10bio *first_r10bio;
   1525	

quoted

1526		while (atomic_dec_and_test(&r10bio->remaining)) {

   1527	
   1528			allow_barrier(conf);
   1529	
   1530			if (!test_bit(R10BIO_Discard, &r10bio->state)) {
   1531				first_r10bio = (struct r10bio *)r10bio->master_bio;

quoted

1532				free_r10bio(r10bio);

   1533				r10bio = first_r10bio;
   1534			} else {
   1535				md_write_end(r10bio->mddev);
   1536				bio_endio(r10bio->master_bio);
   1537				free_r10bio(r10bio);
   1538				break;
   1539			}
   1540		}
   1541	}
   1542	

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